Magnetic system



July 8, 1969 R. DEFAIN MAGNETIC SYSTEM y Filed Feb. a, 1967 xNveNToR:

R DEFA/N @y QA. 34.79.

ATTORNEY K A United States Patent 3,454,838 MAGNETIC SYSTEM RaymondDefaiu, Paris, France, assignor to CSF-Compagnie Generale de TelegraphieSans Fil, a corporation of France I Filed Feb. 2, 1967, Ser. No. 613,498Claims priority, application France, Feb. 18, 1966,

50, Int. Cl. H01h 47/ 00,' Htllf 1/00, 7/20 U.S. Cl. 317--123 14 vClaimsABSTRACT OF THE DISCLOSURE the pole pieces of the main magnet,preferably in the form of sheets of nonmagnetic material.

Background of the invention This invention relates to magneticstructures of the type which includes one or more permanent magnets andtwo pole pieces, for example, of soft iron, secured one to each of twofree ends of the magnet or magnets. More particularly, the invention isconcerned with means for controlling the intensity of the magnetic fieldin the air gap formed by the space separating the two pole pieces.

Structures of this type are known in which the magnetic field in the airgap can be controlled by means of magnetic shunt comprising a mild-steelpiece, displaceable with the aid of an adjustment screw in the region ofthe air gap. To permit field variations within wide limits, the magneticshunt piece must be placed as near as possible to the air gap and, underthese conditions, any variation of the magnetic field in the air gapalso brings about a modification of the field pattern or configuration.Moreover, such systems have the disadvantage that they do not permitfast variations of the field.

In certain applications it is important that the configuration of thelines of force of the magnetic field should remain unchanged while thefield intensity is being adjusted. For example, a substantially xedniagnetic field configuration is required in travelling wave tubes whichmake use of this field either for focusing an electron beam (tubes ofthe so-called O-type) or for propagating au electron beam by themagnetic field associated with a perpendicular electric field (tubes ofthe so-called M-type).

Summary of the invention It is an object of the present invention toprovide an improved magnetic structure in which the above disadvantagesare eliminated or at least effectively reduced.

The present invention consists in a device for controlling the magneticfield intensity in an air gap defined between two pole pieces of apermanent magnet structure, which device4 comprises an electromagnetdisposed with its extremities adjacent the pole pieces with sheets ofnonmagnetic material interposed between the electromagnet and the polepieces, the electromagnet being energized by a controllable currentsource, so that the magnetic field intensity in the air gap can becontrolled by the control of the current supplied to the electromagnet.

In the accompanying drawings:

FIGURE l shows one embodiment of a magnetic system in accordance withthe invention; and

FIGURE 2 shows another embodiment of the invention.

In carrying the invention into effect according to one convenient modeby way of example, FIGURE l shows a magnetic system which includes aU-shaped permanent magnet 1 with two mild-steel pole pieces 2 and 3,fastened respectively to each of the two extremities of magnet 1 an-dforming therewith an air gap 4.

The assembly 1, 2, 3 is provided with a control device comprising aU-shaped electromagnet 5, carrying a wind ing 6 energized by a currentsource 7 in series with a variable resistor (rheostat) 8. A suitablepolarity reversal device of conventional construction, such as a manualor electronic device, may be connected also between the current source 7and its load 6.

Interposed between the outer surfaces of the pole pieces 2 and theelectromagnet 5 are sheets 9 of nonmagnetic material (for example,duralumin), intended to limit the flux portion of magnet 1 derived inelectromagnet 5.

With this disposition, by controlling the direction and the intensity ofthe electric current in the winding 6, it is possible to supply amagnetic flux of a desired intensity and direction passing through theair gap 4, wherein it is added to or subtracted from the ux of thepermanent magnet 1.

It has been vertified experimentally that this system enables themagnetic field intensity in the air gap 4 to be varied within widelimits while the field configuration in the gap remains substantiallyunchanged even for large field variations.

Moreover, the electrical energy required for the control as supplied bythe source 7 is relatively small because slight current variations inthe winding 6 cause significant variations in the reluctance of themagnetic circuit of electromagnet 5, which in turn lead to variations ofthe ux portion of magnet 1 derived in electromagnet 5.

In an embodiment in which the permanent magnet had a length of 11.5 cm.and a cross-section of 20 cm2, and the electromagnet had a length of l5cm. and a cross-section of 7 cm?, it was possible to vary the magneticfield in the air gap of the permanent magnet between 0 and 3600 gausswith an energy of only 40 watts in the electrical circuit of theelectromagnet.

FIGURE 2 shows an embodiment with two air gaps in which the fieldintensity is controllable in one gap and fixed in the other. Theright-hand portion of the structure is here effectively the same as inFIGURE l, but the U-shaped permanent magnet is replaced here by twostraight bar permanent magnets 11 and 12 arranged in special parallelrelationship and two pole pieces 13 and 14 between which there isdefined an air gap 15. Thus, the field intensity is fixed in gap 15 andcontrollable in gap 4.

While I have shown and described only two embodiments according to thepresent invention, it is obvious that the same is not limited theretobut is susceptible of numerous changes and modifications as known to aperson skilled in the art, and I therefore do not wish to be limited tothe details described and illustrated herein but intend to cover allsuch changes and modifications as are encompassed by the scope of theappended claims.

I claim:

1. A device for controlling the magnetic field intensity in an air gapbetween two pole pieces of a magnet structure substantially ywithoutaffecting the field configuration thereof, comprising magnet meanshaving two pole pieces defining therebetween an air gap, and means forcontrolling the magnetic field intensity in said air gap substantiallywithout affecting the field configuration thereof includingelectromagnet means having two end portions placed near and operativelyassociated with said pole pieces.

2. A device according to claim 1, wherein said control means includesmeans for varying the energization of said electromagnet means. l

3. A device according to rclairn 2, further comprising a nonmagneticmaterial interposed between said end portions and adjacent surfaces ofsaid pole pieces.

4. A device according to claim 3, wherein said firstmentioned magnetmeans is a permanent magnet.

5. A device according to claim 4, wherein said magnet means has only asingle air gap which is defined between said two pole pieces.

6. A device according to claim 4, wherein said magnet means has at leasttwo air gaps, one of said air `gaps being defined between said two polepieces and the other air gap being defined by a further break in thestructure of said magnet means.

7. A device according to claim 1, wherein said control means includesmeans for selectively Ivarying or reversing the polarity of theenergization of said electromagnet means.

8. A device according to claim 1, further comprising a nonmagneticmaterial interposed between said end portions and adjacent surfaces ofsaid pole pieces.

9. A device according to claim 1, wherein said firstmentioned magnetmeans is a permanent magnet.

10. A device according to claim 9, wherein said magnet means has only asingle air gap which is defined between said two pole pieces.

11. A device according to claim 9, wherein said magnet means has atleast two air gaps, one of said air gaps being defined between said twopole pieces and the other air gap being defined by a further break intheA structure of said magnet means.

12. A device according to claim 1, wherein said magnet means has only asingle air gap which is defined between said two pole pieces.

13. A device according to claim 1, wherein said magnet means has atleast two air gaps, one of said air gaps being defined between said twopole pieces and the other air gap being defined by a further break inthe structure of said magnet means.

14. A magnet assembly in which the magnetic field intensity in an airgap defined between two pole pieces of a permanent magnet structure isadapted to be controlled, wherein the improvement icomprises anelecromagnet disposed with its extremities adjacent the pole pieces withsheets of non-magnetic material interposed between the electromagnet andthe pole pieces, the electromagnet -bein'g energized by a controllablecurrent source.

References Cited UNITED STATES PATENTS 2,718,606 9/1955 Zuerker 335-2103,069,602 12/1962 Stout 335-236 3,146,381 8/1964 Moreau 335-237 LEE T.HIX, Primary Examiner.

DENNIS HARNISH, Assistant Examiner.

U.S. Cl. X.R. 335-209, 210

